Pan Tilt Zoom (PTZ) dome cameras rotate, tilt and zoom during operation to provide surveillance of an area. These PTZ cameras provide images which are displayed on a screen or monitor or other display device. When the camera is operating, there is often a need to mask “privacy zones”, or specific areas or objects within the field of view of the camera. For example, in a hotel lobby, the privacy zone could include objects such as a swimming pool, or dressing or changing rooms.
During the operation of the PTZ camera, its rotating and zooming features make an object appear to “move” across the screen or display device as the area displayed by the camera changes. Thus the object (or objects) to be masked “moves across the screen” as the camera performs the pan, tilt operation, and the object also “enlarges and/or diminishes” as the zoom operates. FIG. 1 shows a prior art scenario when the tilt angle of the camera is zero. The object to be hidden and the privacy zone both appear to move horizontally across the screen at this low tilt angle. However, at higher tilt angles, generally greater than 45 degrees, the object appears to move in an arc across and down the screen. FIG. 2 shows the prior art scenario when the tilt angle of the camera is 70 degrees. Here the privacy zone still moves horizontally across the screen but the object appears to move in an arc. Thus the object is not continuously masked by the privacy zone, as it is when a low tilt angle is used.
The known PTZ dome and camera combinations in the market today do not work well for privacy zones when the dome camera is operating at higher tilt angles. Due to the geometry of PTZ camera rotation, at higher tilt angles, real objects do not move horizontally across the screen as at lower angles, but rather they follow a curved path. For example, the Honeywell KD6i dome does not address this problem and when using a Sony camera with the KD6i dome, the entire video screen goes blank if any portion, even a tip, of the defined privacy zone overlaps with the new or next camera screen displayed. The overlap leads to sudden screen blanking with complete loss of video, and the user tends to get lost and confused while moving the joystick as he or she has no idea where the camera is looking since he sees only a completely blank monitor screen.
Similarly, the Orbiter Dome of Honeywell and domes of many other manufacturers do not properly account for privacy zones at higher tilt angles due to the above problem. At present, there is no simple equation or solution executable by low end processors without floating point support to achieve the update rates required in real time to correct the above problem. Accordingly, a system and method is needed to maintain the privacy zone so that the object is always masked under the various pan/tilt/zoom conditions of the camera.